Using Horizontal Levees to Buffer the Effects of Sea Level Rise in San Francisco Bay
The Oro Loma Sanitary District (OLSD) constructed a horizontal levee storm surge barrier as a way to address concerns about flood control, water quality, and habitat quality in light of sea level rise and coastal flooding. A horizontal levee uses vegetation planted on a graduated slope to buffer wave energy. In 2019, the East Bay Dischargers Authority (EBDA) and partners began to develop plans to construct another horizontal levee based off of OLSD’s concept just south of the OLSD treatment plant. The EBDA is scheduled to complete the design of the First Mile Horizontal Levee project by January 2023.
The San Francisco Bay Area is at high risk of sea level rise and coastal flooding. These impacts pose threats to coastal infrastructure such as wastewater and stormwater utilities as well as nearby natural ecosystems. In 2015, OLSD began construction on a horizontal levee storm surge barrier to address sea level rise and coastal flooding. The Horizontal Levee Project, completed in 2017, was developed as a demonstration site and “living laboratory,” focused on water quality and monitoring treatment performance. The horizontal levee is a nature-based solution intended to balance flood control, water quality control, and habitat quality concerns. Rather than a vertical wall, a horizontal levee uses vegetation planted on a graduated slope. As sea levels rise, the horizontal levee will enhance sediment accretion, filter pollutants from wastewater treatment effluent, and convert tidal wetlands into upland transitional habitat. The levee requires a freshwater source and wastewater effluent gets reused as part of the last stages of the wastewater treatment process. The demonstration site is about 165 meters in length with one side set about 1.5 meters above the other. The OLSD levee was divided into 12 cells, each of which contain different plant species and soil treatments. The cells are being evaluated to determine which soils and plants best remove pollutants.
In 2019, the EBDA received funds from the U.S. Environmental Protection Agency’s San Francisco Bay Water Quality Improvement Fund through the San Francisco Estuary Partnership’s Transforming Shorelines initiative to develop, design, and permit the full-scale implementation of the First Mile Horizontal Levee Project. This project seeks to build off the success of the OLSD horizontal levee concept, and will be located south of the Oro Loma Wastewater Treatment Plant at Oro Loma Marsh, on land owned by the East Bay Regional Parks District.
The EBDA project has three main objectives: (1) build capacity for nature-based solutions through technical assistance; (2) advance a portfolio of nature-based projects; and (3) advance state-of-the-art water quality improvement approaches. The project aims to build capacity by establishing the Transforming Shorelines Collaborative, regional roundtables, and a toolkit to synthesize lessons learned. The project is funded by $1,480,000 from the U.S. Environmental Protection Agency and ~$1,480,00 from a required non-federal match. The EBDA is also seeking approval of the project from the Federal Emergency Management Agency for flood protection.
Outcomes and Conclusions
OLSD and EBDA are working with a number of partners on these efforts including the University of California Berkeley, the Hayward Area Shoreline Planning Agency (HASPA), Save The Bay, Castro Valley Sanitary District, and the San Francisco Estuary Partnership. Efforts have been made to increase public awareness of the horizontal levee and its effectiveness in reducing wave energy and effluent, particularly items that wastewater treatment does not typically address (e.g., pharmaceutical drugs). UC Berkeley and Save the Bay are working on the monitoring and evaluation piece of the OLSD levee, examining how the plant palette has changed over time. Research has also shown that the pilot levee system is limited by how much water can pass through, and that more cost-effective alternatives are needed to build future levees. OLSD is currently in search of funding to demolish and rebuild the levee using an updated project design. The EBDA is scheduled to complete the design of the First Mile Horizontal Levee project by January 2023.
There have been some concerns over who will implement and maintain the EBDA-designed horizontal levee. While EBDA received a grant for the design of the levee and the East Bay Regional Parks District owns the land the levee would be built on, neither entity is likely to be responsible for levee construction, maintenance, and monitoring over time. Obtaining permits has also been a major challenge, raising concerns over whether the levee will be built.
Others in the San Francisco Bay area are looking at designing horizontal levee projects. For example, the City of Palo Alto and its partners have developed the Palo Alto Horizontal Levee Pilot Project (PAHLPP). Unlike the Oro Loma or EBDA projects, PAHLPP is less focused on wastewater treatment and water quality and more focused on habitat quality and recreation.
Kershner, J. and Braddock, KN. (2021). The East Bay Dischargers Authority and Oro Loma Sanitary Districts efforts to address sea level rise for water utilities [Case study on a project by the East Bay Dischargers Authority and the Oro Loma Sanitary District]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: https://www.cakex.org/case-studies/using-horizontal-levees-buffer-effects-sea-level-rise-san-francisco-bay (Last updated September 2021)